1. Field of the Invention
This invention relates to corrosion inhibitor compositions which are useful in inhibiting corrosion in aerosol products.
2. Description of the Prior Art
Many products designed for household, personal, automotive and other types of use are available as aerosol products. Typical examples of such products include personal products such as hair care products (sprays, coloring agents and styling/conditioning mousses), deodorants, antiperspirants, first aid sprays, and colognes; household products such as waxes, polishes, pan sprays, insecticides and room fresheners; automotive products such as cleaners and polishes; industrial products such as cleaners, lubricants and mold release agents; and animal care products such as tick and flea repellents.
Although some aerosol products are packaged in glass bottles or aluminum cans or lined steel cans, most formulations are loaded into unlined cans made of tin-plated steel. While the tin affords protection against corrosion, the thinness of the coating, imperfections in the surface, wear and tear, and chemical action may ultimately expose the steel to the contents of the can and corrosion can result. When aerosol formulations contain less than about 80 ppm (parts per million) water, corrosion of tin-plate cans is not generally a serious problem. However, if the water content of an aerosol formulation is more than 80 ppm, problems due to corrosion are more likely to occur.
The introduction of dimethyl ether (DME) as an aerosol propellant has opened the way to the use of more water-based aerosol formulations and made possible the manufacture of products of lesser flammability and lower ingredient cost. However, the use of water in such aerosol formulations also increases the problem of corrosion on the interior of the tin-plated steel cans which are so widely used, thus leading to contamination of the aerosol product and ultimately to leaking of the can if corrosion is severe enough. For this reason, corrosion inhibitors are used with aerosol propellants containing DME, when this propellant is to be used in tin-plated steel cans containing a water-based formulation.
The matter of inhibiting corrosion in an aerosol can presents the dual problem of achieving corrosion inhibition in a system where there is both liquid and vapor phase contact with the metal. In a system that contains DME and water, corrosion of the can in areas in contact with the vapor phase is aggravated by the fact that relatively large amounts of water vapor are present along with the DME propellant in the vapor space above the liquid contents of the container. For example, the vapor phase of a95/5 wt % dimethyl ether/water system contains 7,750 ppm water vapor at 70.degree. F. (21.1.degree. C.). Moreover, the addition of ethanol to a DME/water system will often exacerbate the problem of vapor phase corrosion. A 90/5/5 (wt %) DME/ethanol/water system will contain 9,100 ppm water vapor at 70.degree. F.